Post signal modulation in electronic musical instruments



Jan? 1953 H. o. SCHWARTZ ETAL POST SIGNAL MODULATION IN ELECTRONIC MUSICAL INSTRUMENTS Filed May 7, 1965 2 Sheets-Sheet l PIPE-AMP I68 FROM A ME I 78 Jan. 30, 1968 H. o. SCHWARTZ ETAL ,9

POST SIGNAL MODULATION IN ELECTRONIC MUSICAL INSTRUMENTS United States Patent 3,365,993 POST SIGNAL MODULATION IN ELECTRONIC MUSICAL INSTRUMENTS Harold 0. Schwartz, North Tonawanda, and Peter E. Maher, Tonawanda, N.Y., assignors to The Wurlitzer Company, Chicago, IlL, a corporation of Ohio Filed May 7, 1965, Ser. No. 454,134 18 Claims. (Cl. 841.01)

ABSTRACT OF THE DISCLOSURE An electronic musical instrument such as an organ having means for modulation of the signal after generation, illustratively comprising a Schmitt trigger circuit timed to the depression of a key and operative through a light dependent resistor device or a transistor to modulate the signal.

This invention relates to the art of electronic musical production, and most particularly is concerned with modulation of signals after generation thereof to produce percussive effects.

Electronic organs have become quite versatile in operation. Such instruments can simulate other instruments to a greater degree than any other musical instruments. Al-

though an organ generally has a relatively slow build-up of tone intensity at the start of playing a note, it often is desired to produce percussive effects either as percussive organ tones or simulating other instruments. The attack characteristics of an electronic organ can be readily controlled by using proper time constants in connection With an oscillator which is switched on to play a note. However, for rather obvious reasons of economy, it is desirable to use a single generator simultaneously to produce different eifects such as ditferent tonal or footage stops on an organ. Furthermore, the most satisfactory electronic organs from a commercial standpoint use one octave of ex tremely stable master oscillators with a plurality of octaves of divider or slave oscillators controlled thereby. It may be desirable to produce different eifects at the same time from the same tone generator, and this obviously cannot be done if attack and decay characteristics are determined solely by starting and stopping an oscillator. Furthermore, a divider type organ as suggested above would require that oscillators operate continuously;

Accordingly, it is an object of this invention to provide an electronic musical instrument using post-signal modulation, i.e., wave shaping of an electronic oscillation after it has been generated.

It is a further object of this invention to provide improved means for producing percussive effects in an electronic organ.

It is yet another object of the present invention to provide means for producing repetitive percussion in an electronic organ such as for producing banjo effects.

A further object of the present invention is to provide improved means for producing repeating percussion in an electronic musical instrument wherein successive notes played will percuss even though an earlier note continues to play.

.Other objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of an electronic organ incorporating the principles of the present invention;

ice

FIG. 2 is a simplified circuit diagram illustrating the principles of the present invention;

. FIG. 3 is a reproduction of the wave shape produced by the circuit of FIG. 2;

FIG. 4 is a circuit diagram fully illustrating the present invention;

FIG. 4A is a schematic perspective view showing a simple switch arrangement; and

FIG. 5 is a circuit diagram representing a modification of a portion of FIG..4.

Referring now in greater particularity to the figures of .the drawing, and first to FIG. 1, there will be seen an electronic organ 10 embodying the principles of the present invention, and including a case or housing 12 having an upstanding music rack or stand 14. The organ is provided with alower manual or keyboard 16 and an upper manual or keyboard 18, each comprising a plurality of keys, in accordance with the usual practice. Many stop tablets 20 also are provided for selecting various functions of the organ. The organ is provided with a swell pedal 22 for determining the overall volume, and with a pedal clavier 24 for playing the pedal tones. Loudspeakers (not shown) are disposed behind a grill 26 at the front of the organ. Various tone generators and amplifying means (not shown) are disclosed within the organ, more or less in accordance with conventional practice.

Certain of the principles of the present invention are illustrated in simplified fashion in FIG. 2. Thus. a musical tonegenerator is shown as a oscillator 28, which may be considered to be oscillating continuously. The oscillator is connected to a light dependent resistor 30, sometimes known as an LDR. As is known, such a resistor has a very'high resistance when it is kept in the dark, the exact degree of resistance being determined by the particular resistor. On the other hand, when the resistor is exposed to light, its resistance drops quite markedly. The changing resistance is such that the resistance drops quite rapidly when first exposed to light, while the resistance increases somewhat more gradually when the light is extinguished. The light dependent resistor 30 is connected to a junction 32 which leads to an output indicated at 34. The junction 32 is connected to ground by a resistor 36, and this resistor acts with the light dependent resistor to form a voltage divider.

A neon bulb 38 is disposed adjacent the resistor 30, and I a light shield 40 may be placed around the resistor and neon bulb to avoid interaction when other light dependent resistors and neon bulbs are used, and more efiiciently to utilize the light from the bulb. The neon bulb is connected at one side to a grounded resistor 40. The other side is connected to a junction 42 which is grounded through a capacitor 44. A high direct current potential on the order of volts is connected through a resistor 46 to the junction 42. This'resistor acts as a charging resistor, as will be appreciated.

-The circuit in which the neon bulb is connected comprises a well known relaxation oscillator circuit. The capacitor 44 is charged through the resistor 46, and when thecharge reaches a high enough potential, the neon bulb conducts and the capacitor 44 discharges through the neon bulb 38 and the resistor 40 until the capacitor discharges sufliciently for the neon bulb to be extinguished.

During the period when the neon bulb is ignited, the light dependent-resistor 30 is of relatively low resistance, and there is a substantial output at 34. On the other hand, When the neon bulb is dark, the resistance of the light resistor is sufficiently high that there will be relatively little output or even no output, depending on the dark value of the light dependent resistor.

The wave shaft produced by the circuit of FIG. 2 is shown in FIG. 3. The oscillations produced by the tone generator 28 are illustrated at 48 as being of a sinusoidal shape. The envelope, as determined by the light dependent resistor 30, and which modulates the oscillations 48, is indicated at 50. It will be seen that this envelope goes from a minimum at 52 quite rapidly up to a maximum or peak at 54 when the light dependent resistor 30 is exposed to the light of the neon bulb 38. The neon bulb extinguishes quickly and the resistance of the light dependent resistor increases to provide a decaying envelope at 56, again going to the minimum at 52 until the neon bulb again fires and lowers the resistance of the light dependent resistor. It will thus be apparent that the oscillations 48 from the tone generator 28 are modulated by the oscillations of the relaxation oscillator, in particular through the drop in resistance of the light dependent resistor 30 when the neon bulb 38 fires.

The foregoing circuit can be incorporated in the organ 10, whereby the output tones will appear as a repetitive percussion, somewhat in the nature of a banjo, and, indeed indistinguishable therefrom when the proper tone generators and filters are used. In this connection it will be understood that the oscillations from the tone generator 28 have been shown as a sine wave only for illustrative purposes, and that typically the output would be a complex wave. It is to be further understood that the neon bulb could be keyed directly by one of the organ key switches, either being on or oif, and by this means to produce a percussion which is not repetitive.

At the lower righthand corner of FIG. 4 tone generators 58 are shown in a schematic manner, connected through key switches 60 to stops and filters 62. A nonpercussible signal is taken from the stops and filters 62 at a junction point 64, and is coupled through a capacitor 66 to an upper manual non-percussible preamplifier 68. The output of this preamplifier is coupled through a capacitor 70 and a resistor 72 to a junction 74 leading out to the upper amplifier input as indicated at 76.

A line 78 leads from the junction 64 to a resistor 80 which leads to a junction 82. A movable switch contact 90 is alternately engageable with either of the fixed contacts 86, 88. The movable contact 90 and the two fixed contacts 86, 88, bearing in mind the resistor 84 as opposed to the direct connection between the junction 82 and the contact 88, constitue a percussion volume control, generally identified by the numeral 92. The movable switch contact 90 is connected by a wire or line 94 from the percussion circuits shortly to be described.

The post signal modulation device forming the subject matter of the present invention is enclosed within a dash line rectangle, and the entire unit is identified by the numeral 96. This unit comprises near the top center of FIG. 4 a light dependent resistor 98 in proximity to a neon bulb 100, corresponding to the resistor 30 and neon bulb 38 in FIG. 2. There is an additional neon bulb 102 enclosed within a shield 104 having an opening 106 therein so that the bulb 102, which is constantly illuminated when the organ is turned on, might shine on the neon bulb 100. It is known that the operating characteristics of neon bulbs are such that firing is more dependable and uniform when in the presence of light. Both neon bulbs 102, 100 and the light dependent resistor 98 are enclosed within a shield 106 to exclude extraneous light.

The light dependent resistor 98 comprises a part of a voltage divider circuit. One side of the light dependent resistor 98 is connected to a junction 108 which is grounded to a resistor 110. The output line 94 is connected to the junction 108. The other side of the light dependent resistor 98, for brevity hereinafter referred to as an LDR, is connected to a line 112 leading to a junction 114. The junction 114 is grounded through a resistor at 116, and

. also is coupled through a capacitor 118 to the output of an amplifying transistor 120. The transistor is an N-P-N transistor, the capacitor being connected to the collector, and the collector also being connected through a resistor 122 to a junction 124 on a 3+ bus line 126, connected through a decoupling filter, comprising a series resistor 128 and a shunting capacitor 130, the resistor leading to a junction 132 connected to a positive 34 volts, as indicated. The junction 124 also is connected to a resistor 134 leading to the base of the transistor 120, and the base is grounded through a resistor 136. The emitter of the transistor is grounded through a resistor 138, and this resistor is paralleled by a rather large capacitor in series with a resistor 142 which is selected to balance electrolytic capacitor characteristics, being selected from a range of valves used for this purpose.

The junction 144 between the resistors 134 and 136, connected to the base of the transistor 120, is connected to another junction 146 leading to alternate inputs. Thus, the junction 146 is connected through a series capacitor 148, a shunting resistor 150, and a series resistor 152 to a line 154 leading to a fixed switch contact 156. The fixed switch contact 156 is disposed adjacent a fixed switch contact 158 which is connected by a line 160 to a resistor 162 leading to the junction 74 previously mentioned, and leading at 76 to the upper amplifier.

A movable switch contact 164 normally engages the fixed contact 158, but is movable to engage the fixed switch contact 156, the three contacts forming a switch 159. The movable contact 164 is coupled through a series capacitor 166 to an upper manual percussion preamplifier 168, supplied with percussion signals at 170. The signals appearing at 170 are taken from the tone generators, such as the tone generator 58, and are keyed through key switches, such as the key switches identified generally at 60 and taken from the stops and filters 62, as indicated at 172. It will be understood that specifically different key switches and filters are used for the percussion and for the non-pe-rcussible tones, and that the key switches 60 and the stops and filters 62 are intended as a generic showing.

Returning to the junction 146, connection is made through a capacitor 174 to a junction 176 at the output of an amplifying transistor 178. This transistor again is of the N-P-N type, and the connection 176 is to the collector. The junction 176 is connected through a resistor 180 to a junction 182, and this junction is connected through a decoupling filter comprising a shunt capacitor 184 and a series resistor 186 to the junction 132 leading to the positive 34 volts. The junction 182 is connected to a pair of biasing resistors, namely a resistor 188 leading to a unction 190, and the latter being grounded through a resistor 192.

The junction 190 is connected to the base of the transistor 178. The emitter is grounded through a resistor 194, and the resistor 194 is paralleled by a capacitor 196 and a resistor 198, the latter being selected to meet capacrtor variations.

The amplifying stage including the transistor 178 is provided with two different inputs. Thus, the base junction 190 is connected to a junction 200, and this is connected through a capacitor 202 to a filter 204. The filter comprises a grounded resistor 206, and a series resistor 208 leading to a junction 210. The junction is shunted to ground by capacitor 212, and is connected to a series resistor 214 leading to a junction 216, the latter being shunted to ground by a capacitor 218.

The junction 216, which comprises the input of the filter 204, is coupled through a series capacitor 220 and resistor 222 to the movable contact 224 of a bongo percussion switch 226, having also a fixed contact 228 connected through a line 230 to a conductor element 232 of an insulating stop rod 234. Certain of the details of construction of the stop rod will be set forth shortly hereinzzlfter. The stop rod 234 is the 16-foot nonpercussible ro r 5 It is thought perhaps that it would be helpful at the the present time to refer to FIG. 4A for a better understanding of the stop rod and associated parts. As shown in FIG. 4A, the stop rod 234 comprises a cylindrical, elongated rod. This rod preferably is made of a plastic resin material reinforced with glass fibers. A slot is cut in the rod from one end to the other, and the conductor element or wire 232 is secured therein, and thus connected to the lead wire 230. Various tone generators are shown simply as oscillators at 236, but the tone generators are considerably more complex than indicated in FIG. 4A. Movable switch contacts 238 are connected to the generators, and each of these is depressible into engagement with the conductive element 232 to place a corresponding signal on the output wire 230. As will be understood, each of the keys 16, 18 is effective to depress a plurality of vertically aligned movable contacts, such as the contacts 238, so that the signal can be placed on several stop rods at the same time. As is well known, such stop rods can be mounted for rotation about their own axes, so that when a stop is not intended to play, the movable or whisker contacts will engage the insulating material rather than the conductive insert 232.

Returning now to the postsignal modulation unit 96 of FIG. 4, the junction 200 is coupled through a series resistor 2'40 and capacitor 242 to the output of an am'-' plifying transistor 244, specifically the collector thereof. The collector also is connected through a resistor 246 to a junction 248 leading to the junction 182 for supply of positive potential. The transistor 244, as will be seen, again is an N-P-N transistor. The base is connected to a junction 250 on a voltage divider comprising a resistor 252 connected from the junction 248 to the junction 250, and a resistor 254 connected from the junction 250 to ground. The emitter is grounded through a resistor 256.

The input to the transistor 244 comprises a capacitor v 258 connected to the junction 250. A series resistor 260 is connected to the capacitor 258 and to a shunting capacitor 262 and to a series capacitor 264 and series resistor 266 leading to a movable switch contact 268 forming a part of a pizzicato percussion switch 270. The switch is normally open and is engageable with a fixed switch contact 272 grounded through a resistor 274, and also connected to a junction 276. The junction is connected through a resistor 278 to the conductive insert 280 of a stop rod 282. The junction 276 also is connected through a resistor 284 to the conductor insert 286 of a stop rod 288. The stop rod 282 comprises an 8-foot non-percussible rod, and the stop rod 288 comprises a 4-foot non-percussible stop rod. The signal appearing on each of the stop rods 282, 288 (or more specifically the conductive insert 280, 286 thereof) is a square wave, the frequency of the wave on the stop rod 288 being twice that of the frequency on the rod 282. Accordingly, there is a composite wave in the nature of a stair-step wave appearing at the pizzicato percussion switch 270. It will be understood that the wave applied from the stop rod 234 to the bongo percussion switch 226 is also a square wave, but of one half the frequency of the square wave on the stop rod 282.

The resistors 260, 266 and capacitors 262, 264 comprise a wave shaping filter. The filter 204, also provides a certain degree of wave shaping.

One side of the illuminating neon bulb 102 is connected direct to ground. The other side of this neon bulb is connected through a resistor 238 to a junction 241 which is connected to a B+ bus line 243 leading to a source of a positive 170 volts, as indicated at 245. The junction 241 also is connected to a junction 245 which is directly connected to the neon bulb 100. The other side of the neon bulb 100 is connected through a resistor 247 to a junction 251 which is directly connected to a junction 253, the latter being connected to the collector of a transistor 255 which is in the nature of an electronic switch. This transistor, which is an N-P-N transistor, has

the emitter thereof connected to ground through a resistor 257. The junction 251 is grounded to a resistor 259 and a parallel capacitor 261.

A voltage divider resistor 263 is connected to the junction 245 and also to a junction 265, the latter being connected directly to the base of the transistor 255. The junction 265 also is grounded through a second voltage divider resistor 267. The transistor 255 is controlled by a Schmitt trigger circuit 277 which is connected to a capacitor 271, wire 269 and a series resistor 273 to the junction 265.

The Schmitt trigger circuit 277 includes a transistor 279 and a transistor 281. Both transistors are of the N-P-N type. The emitters of both transistors are connected in common to a grounded resistor 283. The collector of the transistor 279 is connected by means of a wire 285 to resistor 287 leading to a positive potential or B+ bus 289, connected through a decoupling filter comprising a shunting capacitor 291 and a series resistor 293 to the junction 132. The collector of the transistor 281 is similarly connected through a resistor 297 to the wire 289.

The base of the transistor 281 is connected to a junction 299, and this junction is connected through capacitor 290 to the collector of the transistor 279. The junction 299 further is connected through a resistor 292 to the emitter of the transistor 281, and hence to the common emitter resistor 283. The resistor 292 is paralleled by a diode 294 polarized in the direction shown to conduct positively from the base to the emitter.

The collector of the transistor 281 is tied back to the base of the transistor 279 by a resistor 296, which also serves as a voltage dividing biasing resistor for the base of the transistor 279, the base further being connected to ground by a resistor 298. A capacitor 300' is connected by a wire 302 to the wire between junction 299 and the capacitor 290. The capacitor 300 further is connected to the movable contact 304 of a normally open switch 306. This switch also has a fixed contact 308 which is connected by a wire 310 to a junction 312. This junction is connected to the previously mentioned coupling capacitor 271, and also to the wire 285. It will be observed that when the switch 306 is closed, the capacitor 300 is connected in parallel with the capacitor 290.

As will be explained in greater detail hereinafter, the transistor 279 is normally conducting, and the transistor 281 of the Schmitt trigger circuit is normally not conducting. Means is provided for keying the Schmitt trigger circuit momentarily to reverse the condition of conduction, whereby to apply a pulse to operate succeeding stages, as also will be set forth hereinafter. Such keying includes a plurality of percussion key switches 314- at the top left corner of FIG. 4. Each of these switches is respectively controlled by one of the organ keys 16, 18, and one switch is provided for each tone that is to be percussible. Each of the key switches 314 is normally open, and the fixed contact thereof is connected to ground. A movable contact is connected to a resistor 316 in each instance to a common collector 318. The common collector 318 is connected to a junction 320, and this junction is connected through a voltage divider resistor 322 to the positive potential source as previously indicated at 245. As will be appreciated, the potential at the junction 320 is that supplied by the source 245, nominally volts when none of the switches 314 is closed. When any of the switches 314 is closed, there is a voltage divider action between the corresponding resistor 316 and the resistor 322, causing a sudden drop to be applied at the junction 320. If the switch is held closed, and another switch 314 is closed, there will be two resistors 316 in parallel, thus reducing the resistance between the junction 320 and ground, and hence again lowering the potential at junction 320. This successive lowering of potential with closing of switches is continued to a significant degree for the closing of several switches in sequence, all previous switches being held closed. It will be appreci- 7 ated that eventually the resistance of the parallel resistors will become sufiiciently low that connection of another resistor in parallel will hardly be significant. However, balanced against this, it must be borne in mind that it is only possible under normal circumstances for the fingers of an organist to close a total of 10 switches at one time, and normally it will be substantially less than this.

The junction 320 is connected to a diode 324 and a paralleling resistor 326, the combination being connected to a coupling capacitor 328 and a series resistor 330, and hence to a junction 333 connected to the base of transistor 279. The junction 332 also is connected through another series resistor 334 and coupling capacitor 336 to the fixed contact 338 of the switch 340, which also includes a movable contact 342. It is to be understood that the movable switch contacts 164, 304, and 342 are ganged together as indicated at 344. All of the movable switch contacts are normally in the raised position shown, and simultaneously lowered to horizontal position.

The movable switch contact 342 is connected through a resistor 344 to the sliding tap 346 on a potentiometer resistor 348. One end of this resistor is grounded, and the other end is connected to a series resistor 350 and a coupling capacitor 352. The capacitor 352 is connected to a tone generator 354, and it will be understood that this is one of the tone generators 58. The specific frequency of the tone generator 354 is not critical. However, as a practical matter, the tone generator Cit having a frequency of 277 c.p.s. is used.

Operation In considering one phase of operation of the post signal modulation unit 96, assume that the switches 340, 159, 306 are in the raised position shown in the drawings. The percussion signal applied at 170 is connected through the switch contacts 164, 158, and the resistor 162 to the input of the upper amplifier at 76. The post signal modulation unit has no effect on this percussion signal. However, if either or both of the pizzicato percussion switch 270 and the bongo percussion switch 226 are closed, the signals will appear at the junction 190, and hence on the base of the amplifying transistor 178. The signals further are applied to the base of the amplifying transistor 120, and from there go to the light dependent resistor 98. In the normal state, the neon bulb 100 is off and no light shines on the light dependent resistor 98, which therefore has a resistance which is very high compared with that of the resistor 110. Accordingly, there is no output at the junction 108 and on the line 94.

It has been noted heretofore that a negative pulse appears on the collector line 318 whenever one of the switches 314 is closed. A negative pulse is readily passed by the diode 324, and the diode prevents feedback. Transistor 279 is normally conducting, and transistor 281 is normally non-conducting. The negative pulse just referred to is applied to the base of the transistor 279, and this transistor is turned off with concomitant turning on of the transistor 281. The condition quickly reverses itself to the initial state, the time being dependent on the time constants of the feedback circuit of the Schmitt trigger 267. It will be apparent that the diode 294 normally ties the base of the transistor 281 to the emitter to hold this transistor off.

When the transistor 279 is rendered non-conducting, the voltage on the collector thereof, and also on the wire 285, rises from a nominal 8.4 volts to a nominal 17.8 volts. Upon reversion of the Schmitt trigger circuit to its initial condition, the collector voltage again drops to 8.4 volts. Thus, a positive pulse is applied to the line 285 and is coupled by the capacitor 271 to the base of the transistor 255.

The transistor 255 is normally off. Hence, the potential at the collector thereof (junction 248) is the same as at the junction 243, namely +170 volts. There is a 30 volt potential across the neon bulb 100, and it does not conduct.

However, when the transistor 255 is turned on in the manner just described, the potential at the junction 253 immediately drops. The neon bulb turns on, thus illuminating the light dependent resistor 98 and rapidly dropping the resistance thereof substantially to zero or to a very low value. The signal input at the junction 114 thus appears at the junction 104, diminishing only slightly in amplitude, and is applied to the switch 92 and hence to the junction 64 and on to the upper amplifier as indicated at 76.

As soon as the Schmitt trigger circuit reverts to its original condition, the transistor 255 stops conducting, and the neon bulb 100 promptly goes out. The light dependent resistor then reassumes its normal high resistance, with a slight delay, causing the output at the junction 108 to decay to Zero.

If the switch contacts 304, 164 and 342 are moved down into respective engagement with the fixed switch contact 308, 156 and 338, the percussion signals from the source 170 are subject to control by the post signal modulation unit 96. The pizzicato percussion and bongo percussion may be switched on or off by the respective switches 270 and 226. As will be apparent, the percussion signals from 170 are connected through the switch contacts 164, 156 to the wire 154, and on to the amplifying transistor and to the input junction 114 of the light dependent resistor 98.

The switch 306 connects the capacitor 300 in parallel with the capacitor 290, the two capacitors being of equal value, namely two mfd. This alters the feedback characteristics of the Schmitt trigger circuit so that it acts as a flip-flop circuit, with one of the transistors 279, 281 con-ducting, and then the other. The repetition rate is controlled by the position of the sliding tap 346 on the potentiometer resistor 48. The frequency of the tone. generator 354 is not particularly significant, except that it should be at least ten times the repetition rate of the Schmitt circuit, which in the present instance is desired to be about 20 cycles per second. However, the amplitude of the signal picked up by the tap 346 does determine the repetition rate. The control .or triggering is somewhat analogous to that of a triggered relaxation oscillator as in a sweep generator.

It will be apparent that the flip-flop action of the Schmitt trigger circuit causes the neon bulb 100 to be turned on and off at a repetitive rate, the rate depending on the setting of the sliding tap 346. This causes the light dependent resistor 98 alternately to have a low resistance and a high resistance, whereby the wave shape appearing at 108 has an envelope similar to that previously discussed in connection with FIGS. 2 and 3.

Although the Schmitt trigger is continuously operating to produce a square wave output on the line 285, it will be understood that whenever one of the switches 314 is closed, the negative pulse produced thereby will cause the transistor 279 to be ofi. This pulse may either hold the transistor 279 off, or turn it off, depending on the point in the cycle at whcih the negative pulse is delivered. In any event, the negative pulse times the cycle so that a cycle starts whenever, the pulse is delivered, whereby the percussion output appearing at 108 is in synchronism with the playing keys. In other words, regardless of the time in which a key is depressed relative to the cycle of the Schmitt trigger circuit, the maximum percussive effect will be obtained immediately, followed by a dropping off of the intensity. The repetitive percussion obtained if a note is played continuously is very similar to that of a banjo or other repetitively plucked or percussed instrument, depending on the stop setting and the filter selected thereby.

The circuit of FIG. 5 comprises substantially a substitution for the light dependent resistor and actuating neon bulb of FIG. 4. Certain numerals have been repeated in FIG. 5 to indicate connections. Thus, the circuit of FIG. 5 includes a transistor 356, the base of which is connected to a junction 358. The junction 358 is connected 9 through a resistor 360 to a line 269, and for purposes of identification, the line between the capacitor 271 and resistor 273 in FIG. 4 has been numbered as 269. The line is connected to ground through a resistor 362. The junction 358 is further connected through a resistor 364 to the junction 132 providing a positive 34 volts. The base thus derives a potential through the voltage divider comprising the resistors, 364, 360 and 362. Further,

the base is pulsed from the Schmitt circuit over the wire 269.

The base of the transistor 356 is shunted to ground by a capacitor 366, and the emitter is directly connected to ground. The collector of the transistor is connected to the junction 108, leading to the output line 94. The junction 108 also is connected through a resistor 366 to the junction 146 receiving input from the upper manual percussible preamplifier 168 and from the pizzicato and bongo percussion (otherwise known as the eifects) amplifier 178. The junction 146 also is connected to ground through a resistor 368.

Operation of the post-signal modulation unit with the substituted circuit portion of FIG. is similar in function to that previously described. The transistor 356 is normally turned on. When it is turned on, the internal resistance from collector to emitter is on the order of no more than 50 ohms. This reistance forms a voltage divider with the resistor 366, and substantially shunts all of the input to ground. On the other hand, when the transistor 356 is pulsed from the Schmitt circuit to turn ofi, the internal resistance of the transistor becomes very high. The voltage divider action then is such that the signal-is applied to the output junction 108 and to the output line 94 substantially without diminution, whereby the signal is modulated in accordance with the pulsed conductivity 'of the transistor 356. The capacitor 366 holds the tran sistor on a short time in decaying fashion to product the desired decay, such as at 56 in FIG. 3.

Necessary circuit values will doubtless occur to those skilled in the art. However, for aid in constructing the invention, exemplary values as used in FIGS. 4 and 5 are set forth hereinafter, R and C respectively being substituted for the words resistor and capacitor for brevity:

Ohms Ohms R72 2.2K R256 680K R80 22K R257 680K R84 56K R259 820K R110 2.2K R260 4.7K

R116 1.5K R263 2.2K

R128 1K R266 4.7K

R134 27K R267 K R136 10K R273 3.9K

R138 680 R274 5.6K R142 1 10 thru 100 R278 33K R150 1.5K R283 560 R152 5.6K R284 68K R162 2.2K R287 1 2K R180 3.9K R292 3 3K R188 47K R293 2 2K R192 4.7K R296 K R194 680 R297 2 2K R198 1 10 thru 100 R298 6 8K R206 560K R316 2.2K

R208 10K R326 270K R214 8.2K R330 2 2K R222 22K R334 2 3 9K R238 220K R344 6 8K R240 10K R350 10K R244 22K R360 33K R246 39K R362 18K R249 82K R364 220K R252 47K R366 15K R254 4.7K R368 4 7K 1 Select.

2 Select 2.2K47K to compensate for C290 and C300.

Mfd. Mfd.

C l00 C264 47 The specific examples of the invention as herein shown and described are for illustrative purposes only. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

1. In an electronic organ comprising a plurality of tone generators for generating electric oscillations corresponding to organ tones, a plurality of keys, a plurality of key switches for controlling the output of said tone generators and operated by said keys, amplifier means for amplifying the oscillations generated by said tone generators, and electro-acoustic transducing means for converting the amplified oscillations into audible organ tones, the combination for modulating said oscillations comprising electric circuit path means interconnecting said tone generators and said amplifying means, said circuit path means being effective selectively to conduct oscillations from said tone generators to said amplifying means and not to conduct oscillations from said tone generators to said amplifying means, and means connected to said circuit path for selectively controlling the conduction thereof, said controlling means comprising a continuously operating oscillator rendering said circuit path means alternately conductive and non-conductive, a plurality .of controlling key switch means respectively operable by said keys, means for producing an electric control parameter upon operation of a key switch means, and means connecting said electric control parameter producing means and said continuously operating oscillator and efiective upon depression of a key and operation of the corresponding controlling key switch means to time said continuously operating oscillator to render said circuit path means conductive irrespective of the time in a cycle at which the controlling key switch means is operated.

2. The combination as set forth-in claim 1, wherein said oscillator is of a type capable of having a cycle started upon impression of a pulse, and further including means for producing a pulse upon operation of a controlling key switch means, and means interconnecting said pulse producing means and said oscillator for applying a pulse to said oscillator upon operation of a controlling key switch means.

3. The combination as set forth in claim 1, and further including means interconnecting one of said tone generators and said oscillator for controlling the frequency of said oscillator.

4. The combination as set forth in claim 3, wherein the frequency of said oscillator is controlled by the amplitude of the oscillation applied thereto from the tone generator, and further including amplitude adjusting means interconnecting said tone generator and said oscillator.

5. In an electronic organ comprising a plurality of tone generators for generating electric oscillations correspondand electro-acoustic transducing means for converting the amplified oscillations into audible organ tones, the combination for modulating said oscillations comprising electric circuit path means interconnecting said tone generators and said amplifying means, said circuit path means including alight dependent resistor interconnecting said tone generators and said amplifying means for controlling the passing of said oscillations, a light source deposed in proximity to said light dependent resistor, an oscillator connected to said light source for cyclically lighting said light source and thereby cyclically to render said light dependent resistor conductive and non-conductive, a plurality of controlling key switch means respectively operable by said keys, means for producing an electric control parameter upon operation of a key switch means, and means interconnecting said electric control parameter producing means and said oscillator and effective upon depression of a key and operation of the corresponding controlling key switch means to synchronize operation of said oscillator to the start of a cycle.

6. The combination as set forth in claim 5, wherein said light dependent resistor is connected in series between said tone generators and said amplifying means, and carries the oscillations.

7. The combination as set forth in claim 6, and further including resistance means connected in circuit with said light dependent resistor and forming therewith a voltage divider network.

8. In an electronic organ comprising a plurality of tone generators for generating electric oscillations corresponding to organ tones, a plurality of keys, a plurality of key switches for controlling the output of said tone generators and operated by said keys, amplifier means for amplifying the oscillations generated by said tone generators, and electro-acoustic transducing means for converting the amplified oscillations into audible organ tones, the combination for modulating said oscillations comprising electric circuit path means interconnecting said tone generators and said amplifying means, electric valve means shunting said circuit path to ground and effective when conducting to short out the oscillations applied to said circuit path means, and means connected to said electric valve means for selectively controlling the conduction thereof, said controlling means comprising an oscillator rendering said valve means alternately conductive and non-conductive, a plurality of controlling key switch means respectively operable by said keys, means for producing an electric control parameter upon operation of a key switch means, and means interconnecting said electric control parameter producing means and said oscillator and effective upon depression of a key and operation of the corresponding controlling key switch means to synchronize said oscillator and start a cycle of oscillation thereof.

9. The combination as set forth in claim 8, wherein said oscillator is continuously oscillating, and wherein synchronizing of said oscillator effects the start of a cycle irrespective of the time in said cycle of operation of said controlling key switch means.

10. In an electronic organ comprising a plurality of tone generators for generating electric oscillations corresponding to organ tones, a plurality of keys, a plurality of key switches for controlling the output of said tone generators and operated by said keys, amplifier means for amplifying the oscillations generated by said tone generators, and electro-acoustic transducing means for converting the amplified oscillations into audible organ tones, the combination for modulating said oscillations comprising electric circuit path means interconnecting said tone generators and said amplifying means, said circuit path means including electronic switch means, said electronic switch means being either on or off, and means connected to said electronic switch means for alternately turning said switch on and on, said controlling means comprising an oscillator, a plurality of controlling key switch means respectively operable by said keys, means for producing an electric control parameter upon operation of a key switch means, and means interconnecting said electric control parameter producing means and said operator and effective upon depression of a key and operation of the corresponding controlling key switch means to synchronize said oscillator to start a cycle thereof.

11. The combination as set forth in claim 10, wherein said electronic switch is connected in series and conducts said oscillations.

12. The combination as set forth in claim 10, wherein said electronic switch is connected in shunt and shorts said oscillations to ground.

13. The combination as set forth in claim it), wherein said oscillator is continuously operating, and wherein operation of a controlling key switch means synchronizes said oscillator to start a cycle irrespective of the time of operation of said controlling key switch means relative to the oscillation of said oscillator.

14. The combination as set forth in claim 10, wherein said oscillator comprises a flip-flop square wave oscillator.

15. The combination as set forth in claim 14, wherein said oscillator comprises a Schmitt trigger circuit capable of producing a single pulse and further has feedback means whereby said Schmitt trigger circuit produces a succession of oscillations.

16. In an electronic organ comprising a plurality of tone generators for generating electric oscillations corresponding to organ tones, a plurality of keys, a plurality of key switches for controlling the output of said tone generators and operated by said keys, amplifier means for amplifying the oscillations generated by said tone generators, and electro-acoustic transducing means for converting the amplified oscillations into audible organ tones, the combination for modulating said oscillations comprising electric circuit path means interconnecting said tone generators and said amplifying means, said circuit path means being effective selectively to conduct oscillations from said tone generators to said amplifying means and not to conduct oscillations from said tone generators to said amplifying means, and means connected to said circuit path for selectively controlling the conduction thereof, said controlling means comprising means for producing pulses, a plurality of controlling key switch means respectively operable by said keys, means interconnecting said controlling key switch means and said pulse producing means for causing said pulse-producing means to produce a pulse upon operation of said key switch means when any of said keys is depressed, and means interconnected with said pulse-producing means to cause said pulse-producing means to produce a series of pulses.

17. The combination as set forth in claim 16, wherein operation of a controlling key switch means causes said pulse-producing means to produce a pulse and thereafter to continue the production of a series of pulses when said series pulse-producing means is operated.

18. The combination as set forth in claim 16, and further including means interconnecting a tone generator and said pulse-producing means to control the repetition of a series of pulses.

References Cited UNITED STATES PATENTS 3,229,019 1/1966 Peterson 841.24 X 3,267,196 8/1966 Welsh et al 84-l.24 X 3,309,454 3/1967 Cutler et al 84-l.26 X 3,316,341 4/1967 Peterson 84121 X ARTHUR GAUSS, Primary Examiner.

B. P. DAVIS, Assistant Examiner. 

